FORM 2
THE PATENTS ACT, 1970 (39 of 1970)
As amended by the Patents (Amendment) Act, 2005
&
The Patents Rules, 2003
As amended by the Patents (Amendment) Rules, 2006
COMPLETE SPECIFICATION (See section 10 and rule 13)
TITLE OF THE INVENTION
Brushless DC motor driven ceiling fan
APPLICANTS
Crompton Greaves Limited, CG House, Dr Annie Besant Road, Worli, Mumbai - 400 030, Maharashtra, India, an Indian Company
INVENTORS
Alakkal Kizhakkethil Sivadas, Crompton Greaves Ltd, CG Global R&D Centre, Kanjur (E), Mumbai 400042, Maharashtra, India and Jaishankar Sidhanand Nirody, A-l, Nandavan, Opposite Ambaji Dham, M G Road, Mulund West, Mumbai 400 080, Maharashtra, India, both Indian nationals
PREAMBLE TO THE DESCRIPTION
The following specification particularly describes the nature of this invention and the manner in which it is to be performed:

FILED OF THE INVENTION
This invention relates to a brushless DC motor driven ceiling fan,
BACKGROUND OF THE INVENTION
A brushless DC motor driven ceiling fan comprises a motor housing formed of a bottom end shield and a top end shield fitted together and a fan shaft extending into the motor housing with the end shields rotatably mounted to the fan shaft. A plurality of fan blades are mounted on the top end shield in radially spaced apart relationship with one another. A rotor comprising a plurality of permanent magnets is disposed within the motor housing and fitted to the top end shield. A wound stator is disposed within the rotor describing a clearance with the rotor and mounted to the lower end of the fan shaft. The fan also comprises a control unit having a printed circuit board disposed outside the motor housing and mounted to the fan shaft. The printed circuit board comprises an electronic controller. Hall sensors for sensing rotor poles are located in the motor housing and connected to the electronic controller. The stator winding is also connected to the electronic controller. The electronic controller is further connected to a power supply. Such a fan construction comprises a large number of connections namely hall sensors to the electronic controller, stator winding to .the electronic controller and electronic controller to the power supply. It is cumbersome and troublesome to carry out too many connections. Further, the connections require extra length of wires and increase the cost. In order to overcome the above problems, fan designs were developed in which the printed circuit board comprising the electronic controller was mounted within the motor

housing. Brushless DC motor driven ceiling fans comprising electronic controller located within the motor housing are described in our patent application No 1166/MUM/2006 filed on 21 July 2006 and patent application No 649/MUM/2008 filed on 26 March 2008. In such fan designs, lead wires connecting the hall sensors to the electronic controller have been eliminated. However, during working of the fan, the stator winding and electronic devices of the electronic controller get heated up. As a result, there is excess heat development within the motor housing. Due to excess heat development within the motor housing, the electronic controller may start malfunctioning thereby reducing the reliability of the fan. In order to withstand high temperature within the motor housing, it is possible to have electronic controller comprising electronic devices having high temperature withstanding capability but such devices are expensive thereby increasing the cost of the fan. Further, the serviceability and repairability of the fans comprising electronic controllers within the motor housing are poor. There are also brushless DC motor driven ceiling fans comprising a control unit having a printed circuit board with electronic controller mounted outside the motor housing along with optocouplers for sensing the rotor speed. Optocouplers are very sensitive to dust. As the optocouplers are located outside the motor housing, dust will accumulate on the optocouplers thereby reducing the sensitivity and reliability of the optocouplers. Due to accumulation of dust, the optocouplers will start malfunctioning over a period of time thereby reducing the reliability of the fan. Due to accumulation of dust over a period of time, the optocouplers may stop functioning thereby rendering the fan non-operational.

OBJECTS OF THE INVENTION
An object of the invention is to provide a brushless DC motor driven ceiling fan which is cost effective and reliable.
Another object of the invention is to provide a brushless DC motor driven ceiling fan which has excellent serviceability and repairability.
DETIALED DESCRIPTION OF THE INVENTION
According to the invention there is provided a brushless DC motor driven ceiling fan comprising a motor housing formed of a top end shield and a bottom end shield fixed together and a hollow fan shaft extending into the motor housing with the bottom end shield and top end shield rotatably mounted to the fan shaft, a plurality of fan blades mounted to the top end shield in radially spaced apart relationship with one another, a rotor disposed within the motor housing and mounted to the top end shield, the rotor comprising a plurality of permanent magnets, a wound stator disposed within the rotor describing a clearance with the rotor and mounted to the lower end of the motor shaft, an electronic controller comprising a printed circuit board is disposed outside the motor housing and fitted to the fan shaft, Hall sensors for sensing rotor poles are mounted at the bottom surface of the printed circuit board and a magnetic sensor is disposed directly below the hall sensors and mounted on the outer surface of the top end shield, the magnetic sensor being a replica of the rotor and comprising a plurality of permanent

magnets corresponding to the rotor magnets, the stator winding being connected to the electronic controller by lead wires extending through the shaft and the electronic controller being connected to a power supply through lead wires and an enclosure for the printed circuit board mounted to the fan shaft.
The following is a detailed description of the invention with reference to the accompanying drawings, in which:
Fig 1 is a crossectional view of a brushless DC motor driven fan according to an embodiment of the invention;
Fig 2 is a crossectional view of the enclosure and the printed circuit board of the fan of Fig l;
Fig 3 is a plan view of the top end shield of the fan of Fig 1;
Fig 4 is a partial crossectional view of the shaft of the fan; and
Fig 5 is a scrap crossectional view of the top end shield and printed circuit board of the fan of Fig 1.
The ceiling fan 1 as illustrated in Fig 1 to 5 of the accompanying drawings comprises a motor housing 2 formed of a top end shield 3 and a bottom end shield 4. The top end

shield comprises an inverted cup shaped central portion 5 with a shaft hole 6 therein. The top end shield also comprises a laterally projecting portion 7 projecting laterally from the inverted cup shaped central portion. The outer end of the laterally projecting portion describes a downward portion 8 and a laterally extending portion 9. 10 is a cylindrical portion projecting downwardly from the laterally projecting portion concentric with the inverted cup shaped portion. 11 is a saucer shaped bottom end shield. The top and bottom end shields are fixed together with screws 12. A plurality of fan blades 13 are mounted to the top end shield in radially shaped apart relationship with one another with rivets 14. 15 is a hollow fan shaft extending into the motor housing with the bottom end shield and top end shield mounted to the fan shaft using bearings 16 and 17 respectively. 18 is a rotor disposed within the motor housing and fitted to the inner surface of the cylindrical portion 10 of the top end shield. The rotor comprises a plurality of permanent magnets 19. 20 is a wound stator disposed within the rotor describing a clearance with the rotor and mounted to the lower end of the fan shaft. The clearance between the rotor and stator is not marked in the drawings but can be seen in Fig 1.21 is a spring disposed over the lower end of the fan shaft and held between the stator and bearing 16 to keep the stator in position on the fan shaft and prevent the stator from sagging down on the fan shaft. 22 is an electronic controller comprising a printed circuit board disposed outside the motor housing and having a shaft hole which has not been marked in the drawings but can be seen in Figs 1 and 2. The lower portion of the fan shaft comprises an engaging circumferential groove 26. The inner edge of the printed circuit board surrounding the shaft hole therein is snap fitted in the engaging groove on the fan shaft so as to hold the printed circuit board on the fan shaft. Hall sensors 27 are mounted at the bottom surface

of the printed circuit board. 28 is a magnetic sensor disposed directly below the hall sensors and mounted on the outer surface of the laterally projecting portion 7 of top end shield. The magnetic sensor is a replica of the rotor and comprises a plurality of equal number of permanent magnets 29 corresponding to the rotor magnets. The stator winding is connected to the electronic controller by lead wires 30 extending through the fan shaft vide side openings 31 and 32 in the fan shaft. The electronic controller is connected to a power supply (not shown) through lead wires 33 extending through down rod 34 of the fan. The down rod and fan shaft are fitted together. 35 is an enclosure comprising a central tubular portion 36 disposed over the fan shaft and fitted to the fan shaft by tightening grub screw 37 in a mounting hole in the tubular portion and a corresponding mounting hole in the fan shaft. The mounting holes in the tubular portion and fan shaft have not been shown in the drawings but can be visualized in Figs 1 and 2. The enclosure also comprises a lateral extension 38 extending radially from the lower end of the tubular portion, a raised portion 39 extending upwardly from the outer end of the lateral extension and a downwardly extending portion 40 extending downwardly from the top of the raised portion. The lower end of the downwardly extending portion is tapered marked 41. 42 is a lug projecting down from the inner surface of the downwardly extending portion 40 of the enclosure. The distal end of the lug has a laterally extending tapered portion 43. The outer end of the printed circuit board is slid up against the tapered portion 43 of the lug 42 past the tapered portion and snap fitted against the tapered portion of the lug so that the outer end of the printed circuit board is well supported in the lug. 44 is bottom canopy of the fan fitted over the bottom down rod of the fan and resting on the lateral extension 38 of the enclosure against the raised portion 39 thereof. During

operation of the fan, the electronic controller senses the rotor position based on the input from the hall sensors which in turn sense the rotor position through the sensor magnet.
According to the invention the printed circuit board with the electronic controller is located outside the motor housing but well enclosed within the enclosure 35. The atmospheric air can freely enter the enclosure and keep the electronic controller well cooled. At the same time the enclosure also protects the printed circuit board and prevents dust and other foreign particles getting deposited on the electronic controller. As the electronic controller is disposed outside the motor housing, heat development within the motor housing due to generation of heat in the stator winding does not affect the performance of the electronic controller. As a result the performance efficiency and reliability of the fan is improved. As the printed circuit board is located outside the motor housing, serviceability and rapairability of the fan are also good. The invention eliminates lead wires for connecting the hall sensors to the printed circuit board and is also cost effective.
It is understood that the fan shaft need not be fully hollow but can be partially hollow to conceal the lead wires. The number of hall sensors can vary depending upon the controller configuration. Such configurations of the invention are to be construed and understood to be within the scope of the invention.

We claim:
1. A brushless DC motor driven ceiling fan comprising a motor housing formed of a
top end shield and a bottom end shield fixed together and a hollow fan shaft extending
into the motor housing with the bottom end shield and top end shield rotatably mounted
to the fan shaft, a plurality of fan blades mounted to the top end shield in radially spaced
apart relationship with one another, a rotor disposed within the motor housing and
mounted to the top end shield, the rotor comprising a plurality of permanent magnets, a
wound stator disposed within the rotor describing a clearance with the rotor and mounted
to the lower end of the motor shaft, an electronic controller comprising a printed circuit
board is disposed outside the motor housing and fitted to the fan shaft, hall sensors for
sensing rotor poles are mounted at the bottom surface of the printed circuit board and a
magnetic sensor is disposed directly below the hall sensors and mounted on the outer
surface of the top end shield, the magnetic sensor being a replica of the rotor and
comprising a plurality of permanent magnets corresponding to the rotor magnets, the
stator winding being connected to the electronic controller by lead wires extending
through the shaft and the electronic controller being connected to a power supply through
lead wires and an enclosure for the printed circuit board mounted to the fan shaft.
2. The ceiling fan as claimed in claim 1, wherein the enclosure comprises a central
tubular portion disposed over the fan shaft and adapted to be fitted to the fan shaft, a
lateral extension extending radially from the lower end of the tubular portion, a raised
portion extending upwardly from the outer end of the lateral extension and a downwardly

extending portion extending downwardly from the top end of the raised portion, the lower end of the downwardly extending portion being tapered and a lug projecting down from the inner surface of the downwardly extending portion, the distal end of the lug having a laterally extending tapered portion.
3. The ceiling fan as claimed in claim 2, wherein the tubular portion of the enclosure "comprises a mounting hole and is fitted onto the fan shaft by tightening a grub screw in the mounting hole in the tubular portion and a corresponding mounting hole in the shaft.
4. The ceiling fan as claimed in anyone of claims 1 to 3, wherein the printed circuit board comprises a shaft hole therein, the hall sensors being mounted at the bottom surface of the printed circuit board, the shaft having a circumferential engaging groove and the inner edge of the shaft hole in the printed circuit board being adapted to snap fit in the engaging groove on the shaft.
5. The ceiling fan as claimed in anyone of claims 1 to 4, wherein the top end shield comprises an inverted cup shaped central portion with a shaft hole therein, a laterally projecting portion projecting laterally from the inverted cup shaped central portion, the outer end of the laterally projecting portion describing a downward portion and a laterally extending portion and a cylindrical portion projecting downwardly from the laterally projecting portion concentric with the inverted cup shaped portion, the rotor being mounted at the inner surface of the cylindrical portion and the magnetic sensor

being mounted on the outer surface of the laterally projecting portion directly below the hall sensors and the bottom end shield is saucer shaped.